1. Field of the Invention
This invention relates to a radar apparatus on board of a vehicle, etc., and in particular to a radar data processing method capable of measuring the relative distance and relative speed of a target and a radar apparatus using the method.
2. Description of the Related Art
A radar apparatus on board of a vehicle, etc., has a target distance range of about several m to 200 m and it is advisable to provide the radar apparatus with one antenna used for both transmission and reception, so that the radar apparatus is miniaturized; it is preferable from the viewpoint of installation of the radar apparatus in a vehicle, etc. As a radar data processing method satisfying such demands, an FMICW (frequency modulated interrupted continuous wave) method can be named.
FIG. 15 is a diagram to show the basic configuration of a radar apparatus in a related art using the FMICW method.
In the figure, a radar apparatus 1 comprises a control section 2 for generating various control signals, a modulated waveform generation section 33 for generating modulated waveforms of up phase (modulation frequency rise period) and down phase (modulation frequency fall period) based on the control signals from the control section 2, a voltage-controlled oscillator (VCO) 4 for generating a VCO signal of up phase and a VCO signal of down phase in response to output signals from the modulated waveform generation section 33, and switches 5 and 6 having moving terminals connected to the VCO 4 and an antenna 7 installed so as to track a target 8, terminals t connected to each other, and terminals r connected to distribution circuits 9b and 9a described later.
The switches 5 and 6 are controlled by the control section 2 and repeat the operation of connecting to the t terminals for preset time .tau. and connecting to the r terminals for preset time T-.tau. in synchronization with each other, as shown in FIG. 17.
One output terminal of the distribution circuit 9a is connected to one input terminal of a mixer 11a and the other output terminal of the distribution circuit 9a is connected to one input terminal of a mixer 11b. One output terminal of the distribution circuit 9b is connected to the other input terminal of the mixer 11a and the other output terminal of the distribution circuit 9b is connected to the other input terminal of the mixer 11b via a phase-shift circuit 10.
Output terminals of the mixers 11a and 11b are connected to A/D converters 12a and 12b each for converting an analog signal into a digital signal. The digital signals provided by the A/D converters 12a and 12b are stored in memories 13a and 13b.
Output terminals of the memories 13a and 13b are connected to a signal processing section 14 and an output terminal of the signal processing section 14 is connected to a display section 15.
The components 9 to 15 are also contained in the radar apparatus 1.
FIG. 16 shows the frequencies of the signals relative to the time in the FMICW method. Hereinafter, the modulation phase in which the frequency becomes higher with the passage of time will be called up phase and the modulation phase in which the frequency becomes lower with the passage of time will be called down phase.
In FIG. 16, a VCO signal 16a of up phase and a VCO signal 16b of down phase are signals generated from the VCO 4 and a transmission signal 17a of up phase and a transmission signal 17b of down phase are signals emitted from the VCO 4 through the antenna 7 into the air for the time .tau. for which the switches 5 and 6 connect to the t terminals.
A local signal 18a of up phase and a local signal 18b of down phase are signals input from the VCO 4 to the distribution circuit 9b for the time T-.tau. for which the switches 5 and 6 connect to the r terminals. A reception signal 19a of up phase and a reception signal 19b of down phase are signals received at the antenna 7 with a delay of a predetermined time after the transmission signals for the time T-.tau. for which the switches 5 and 6 connect to the r terminals, and input to the distribution circuit 9a. A beat signal 20a of up phase and a beat signal 20b of down phase are signals provided by mixing the local signals 18a and 18b and the reception signals 19a and 19b by the mixers 11a and 11b.
FIG. 17 shows the terminal connection timings in the switches 5 and 6 relative to the time. Assuming that the total time for which the switches 5 and 6 connect to the t and r terminals is T=(n+1).tau., the switches 5 and 6 are controlled by the control section 2 and repeat the operation of connecting to the t terminals for the preset time .tau. and connecting to the r terminals for the preset time T-.tau. in synchronization with each other, as described above.
FIG. 18 shows sample data of up phase and down phase in the memories 13a and 13b in FIG. 15. When the transmission signal 17a and 17b in FIG. 16 are sampled at timings R1-Rn, data pieces P1-Pn are read accordingly and an up-phase data matrix 21a and a down-phase data matrix 21b each consisting of rows P1-Pn and columns R1-Rn in the lower portion of FIG. 18 are provided on the memories 13a and 13b.
FIG. 19 is a block diagram to show the basic configuration of the signal processing section 14 in FIG. 15.
In FIG. 19, the signal processing section 14 comprises a signal processing control section 22 for performing signal processing as shown in FIG. 20 described later, frequency analysis sections 23a and 23b for analyzing frequency spectra from up-phase data and down-phase data from the memories 13a and 13b at the preceding stage under the control of the signal processing control section 22, signal detection sections 24a and 24b for detecting frequencies of spectra detected as target by the frequency analysis sections 23a and 23b under the control of the signal processing control section 22, a combination search section 25 for making a search for a desired combination from the frequencies of the spectra detected by the signal detection sections 24a and 24b under the control of the signal processing control section 22, and a speed measurement section 26 for measuring target relative speed of the combination search section 25 under the control of the signal processing control section 22.
Next, the general operation of the radar apparatus in FIG. 15 will be discussed.
The FMICW method uses a frequency-modulated continuous wave in an interrupted manner.
Under the control of the control section 2 in the radar apparatus 1, a modulated waveform consisting of up phase and down phase generated by the modulated waveform generation section 33 is input to the VCO 4 and becomes the VCO signal 16 shown in FIG. 16, then the VCO signal 16 is input to the switch 5. The switches 5 and 6 are controlled by the control section 2 and repeat the operation of connecting to the t terminals for the preset time .tau. and connecting to the r terminals for the preset time T-.tau. in synchronization with each other, as shown in FIG. 17.
First, in the up phase, the VCO signal 16 from the VCO 4 with the switches 5 and 6 connecting to the t terminals for the time .tau. becomes the transmission signal 17 in FIG. 16 and the transmission signal 17 is input via the switches 5 and 6 to the antenna 7 from which it is emitted in the air. The transmission signal 17 emitted in the air is applied to a target 8 being at one relative distance R and moving at one relative speed V and a part of the transmission signal 17 is reflected.
The reflected wave is shifted by Doppler frequency Fv responsive to the relative speed V and is received at the antenna 7 at the time with a delay of K.tau.=2R/c (c is radio wave speed) after the transmission signal 17, then becomes the reception signal 19 in FIG. 16 and the reception signal 19 is input to the distribution circuit 9a via the switch 6 connecting to the r terminal for the time T-.tau.. The distribution circuit 9a divides the input signal into two parts and feeds the signal parts into the mixers 11a and 11b.
On the other hand, the VCO signal 16 via the switch 5 connecting to the r terminal for the time T-.tau. is input to the distribution circuit 9b as the local signal 18 in FIG. 16. The distribution circuit 9b divides the input signal into two parts and feeds the signal parts into the mixer 11a and the phase-shift circuit 10, which then shifts the phase of the input signal by .pi./2 radian and outputs the resultant signal to the mixer 11b.
The reception signal 19 and the local signal 18 input to the mixers 11a and 11b are mixed in the period of K.tau. to (K+1).tau. in the time T-.tau. into beat signal 20 with the frequency difference between the reception signal 19 and the local signal 18 appearing as a frequency.
At this time, the beat signal 20 provided by the mixer 11a corresponds to the real part of a complex signal and the beat signal 20 provided by the mixer 11b corresponds to the imaginary part of a complex signal, thus the beat signal 20 is provided as a complex signal.
Also in the down phase, beat signal 20 is provided as in the up phase described above.
At this time, letting the beat signal 20 in the up phase be Sup(t), Sup(t) is represented by the following expression (1) and letting the beat signal 20 in the down phase be Sdn(t), Sdn(t) is represented by the following expression (2):
[Expression1] EQU Sup(t)=A.sub.up eIp(j2.pi.U.t+.phi..sub.up)=A.sub.up sin(2.pi.U.t+.phi..sub.up)+jA.sub.up cos(2.pi.U.t+.phi..sub.up)(1) EQU Sdn(t)=A.sub.dn eIp(j2.pi.D.t+.phi..sub.dn)=A.sub.dn sin(2.pi.D.t+.phi..sub.dn)+jA.sub.dn cos(2.pi.D.t+.phi..sub.dn)(2)
where ##EQU1## Aup, Adn: Amplitude term, .phi.up, .phi.fn: Phase term, B: Frequency modulation width, c: Light speed, T: Modulation period, R: Target relative distance, .lambda.: Radar carrier wave length, V: Target relative speed
The beat signal 20 is sampled by the A/D converter 12 every .tau. and is stored in the memory 13. At this time, n sampling results following data P1 representing the transmission signal 17 for each phase are stored in order as (P1, R1), (P1, R2), (P1, R3), . . . , (P1, Rn), as shown in FIG. 18.
Likewise, n sampling results following data P2 representing the transmission signal 17 are also stored in the memory 13 in order as (P2, R1), (P2, R2) , (P2, R3), . . . , (P2, Rn), where Rk (k=1-n) contains the signal of the target at a relative distance in the range indicated by the following expression (5):
[Expression 2] ##EQU2##
At the time at which sampling for data Pm terminates, the signal processing section 14 reads data from the memory 13 and starts signal processing under the control of the control section 2.
Next, the detailed operation of the signal processing section 14 will be discussed with reference to FIG. 20 to show a signal processing procedure of the signal processing section 14 and FIG. 21 to show input/output of the frequency analysis section 23 in the signal processing section 14.
FIG. 21 shows input signals 27a-27c to the frequency analysis section and output signals 28a-28c from the frequency analysis section.
First, at step ST1, the signal processing control section 22 sets its internal counter (variable) k=1.
At step ST2, under the control of the signal processing control section 22, the frequency analysis section 23a reads data P1-Pm in column Rk from the up-phase data matrix 21a in FIG. 18 and finds a frequency spectrum as output signal 28 from input signals P1-Pm27 as shown in FIG. 21 by performing FFT (fast Fourier transform), etc., for example, for the data, then outputs the frequency spectrum to the signal detection section 24a.
At step ST3, under the control of the signal processing control section 22, the signal detection section 24a executes signal detection using CFAR (constant false alarm rate) detection, for example, for the input frequency spectrum, finds frequencies U1, U2, . . . , Up of the spectrum detected as the target, and outputs the frequencies to the combination search section 25.
At step ST4, under the control of the signal processing control section 22, the frequency analysis section 23b reads data P1-Pm in column Rk from the down-phase data matrix 21b in FIG. 18 and finds a frequency spectrum by performing FFT, etc., for example, for the data, then outputs the frequency spectrum to the signal detection section 24b.
At step ST5, under the control of the signal processing control section 22, the signal detection section 24b executes signal detection using CFAR detection, for example, for the input frequency spectrum, finds frequencies D1, D2, . . . , Dq of the spectrum detected as the target, and outputs the frequencies to the combination search section 25.
Next, at step ST6, under the control of the signal processing control section 22, the combination search section 25 combines the input frequencies U1, U2, . . . , Up and D1, D2, . . . , Dq and makes a search for combination Cij (Ui, Dj) in which relative distance R found according to expression (6) mentioned below becomes the range of Rk shown in the above-mentioned expression (5).
If the combination is found, control goes to step ST7 at which the combination search section 25 outputs the relative distance R found at the search time to the display section 15 in FIG. 15 and outputs the combination Cij (Ui, Dj) to the speed measurement section 26.
[Expression 3] ##EQU3##
Further, at step ST7, the speed measurement section 26 uses the following expression (7) to find relative speed V of the target from the input combination Cij (Ui, Dj) and outputs the relative speed V to the display section 15 in FIG. 15:
[Expression 4] ##EQU4##
The display section 15 displays the input relative distance R and relative speed V as information using text or an image on a CRT, for example.
At step ST8, the signal processing control section 22 adds one to the counter variable k. At step ST9, the signal processing control section 22 compares the value of the counter variable k with n. If the value of the counter variable k is less than n, the signal processing control section 22 causes the frequency analysis section 23a to again execute step ST2; if the value of the counter variable k is greater than n, the signal processing control section 22 terminates the process.
The described radar apparatus in the related art can find the relative distance and relative speed of the target with no problem if one detection result is produced at Rk (k=1-n) in each phase.
In fact, however, more than one detection result may be produced at each Rk. When the combination search section 25 makes a search for the combination Cij (Ui, Dj) for the same target at step ST6 in FIG. 20, it cannot make a search for all combinations in real time; the relative distance and relative speed of the target cannot be found in spite of detection in detection processing.